【作者】 杨涛；

【导师】 宫丰奎；

【作者基本信息】 西安电子科技大学 ， 通信与信息系统， 2018， 硕士

【摘要】 正交频分复用(Orthogonal Frequency-Division Multiplexing,OFDM)技术因其具有高自由度、高频谱利用率、强抗多径衰落能力等诸多优点而在多种通信领域中扮演着越来越重要的角色。而随着“一带一路”战略的顺利实施,基于OFDM的海上无线通信技术越来越受到社会的广泛关注。但是,一方面目前国内外还没有针对海上传输环境提出一套完整的信道建模标准,OFDM技术在海上信道中的性能表现尚不明确。另一方面,在海上多径信道中,数据到达接收端的时间不同,导致接收端难以估计出每一帧的正确起始位置,从而造成定时估计出现偏差。同时,船体间的相对运动以及收发晶振的不匹配都会引起频率偏差。因此,为保证在接收端能正确进行数据解调,必须要对定时偏差和频率偏差进行估计和补偿。本文在建立海上无线信道模型基础上,重点对OFDM系统中定时同步和频率同步技术进行深入研究,主要包括:1)在小尺度物理光学(Physical Optics,PO)模型的基础上,首次考虑了海浪高度对接收信号的影响以及船体之间相对运动引起的多普勒效应,提出适用于海上无线通信的动态多径信道模型。提出的模型相较于PO模型,更加全面、真实地反映了海上实际通信信道特性。2)针对海上信道下的定时同步问题,在分析经典定时偏差估计算法在海上信道环境中性能表现的基础上,提出了一种基于恒包络零自相关(Constant Amplitude Zero Auto Correlation,CAZAC)序列的改进训练序列结构。该序列结构着重解决了原算法在系统中存在频偏且频偏值整数部分为奇数时定时不准确的问题。仿真结果表明,无论系统中是否存在频偏,所提算法相较于原算法都能准确找到定时位置。3)针对海上信道下的频偏估计问题,在分析经典频偏估计算法在海上信道环境中性能表现的基础上,提出了一种基于子载波间干扰(Inter Carrier Interference,ICI)自抵消技术的频偏估计算法。该算法在Moose算法基础上通过重新设计导频序列并在接收端引入自抵消技术,降低了ICI对接收信号的影响,从而提高频偏估计精度。仿真结果表明,在海上动态多径信道模型中,所提算法相较于Moose算法,性能提升约为3dB。4)面向海上无线通信环境针对OFDM系统物理层接收机同步模块整体方案完成FPGA实现。并针对帧同步模块提出了一种降低硬件实现复杂度的方案。该方案通过重新定义判决函数,使得每一次的复数乘法运算都可以省去两次加法运算。结果表明,提出方案在FPGA查找表和寄存器资源占用上相比原方案各减少了49.7%和32.8%。更多还原

【Abstract】 Orthogonal Frequency-Division Multiplexing(OFDM)technology plays an increasingly important role in various communication fields since it has lots of advantages such as high degree of freedom,high spectral efficiency,and strong resistance to multi-path fading.With the successful implementation of the "Belt and Road Initiative",the maritime wireless communication technology based on OFDM has attracted more and more attention.However,on the one hand,a complete channel modeling standard for maritime transmission environment has not been proposed at home and abroad,and the performance of OFDM technology in maritime channels is not yet clear.On the other hand,in maritime multipath channel,the time which data arrives at the receiver is different,which makes it difficult for the receiver to estimate the correct starting position of each frame,thereby causing timing estimation offset.Meanwhile,the relative motion between hulls and the mismatch of the sending and receiving crystals cause frequency offset.In order to ensure correct data demodulation at receiver,timing and frequency offset must be estimated and compensated.Based on the proposed maritime wireless channel model,this paper focuses on the in-depth research of timing and frequency synchronization technologies in OFDM system,including: 1)on the basis of the small-scale Physical Optics(PO)model,the influence of the wave height on the received signal and the Doppler effect caused by the relative motion between hulls are considered for the first time,and a dynamic multi-path channel model suitable for maritime wireless communication is proposed.Compared with the PO model,the proposed model more fully and truly reflects the actual communication channel characteristics at sea.2)aiming at the problem of timing synchronization in the maritime channel,based on the analysis of the performance of the classical timing offset estimation algorithm in the maritime channel environment,an improved training sequence structure based on Constant Amplitude Zero Auto Correlation(CAZAC)sequence is proposed.This sequence structure focuses on solving the problem that the original algorithm can’t estimate the correct starting position when there is frequency offset in the system and the integer part of the frequency offset value is an odd number.Simulation results show that the proposed algorithm can accurately find the timing position compared with the original algorithm whether or not there is frequency offset in the system.3)aiming at the problem of frequency offset estimation in the maritime channel,based on the analysis of the performance of the classical frequency offset estimation algorithm in the maritime channel environment,a frequency offset estimation algorithm based on the Inter Carrier Interference(ICI)self-cancellation technique is proposed.Based on the Moose algorithm,this algorithm redesigns the pilot sequence and introduces self-cancellation technology at receiver to reduce the influence of ICI on the received signal,thereby improving the accuracy of frequency offset estimation.Simulation results show that in the dynamic multipath channel model at sea,compared with Moose algorithm,the proposed algorithm has a performance improvement of about 3dB.4)aiming at the maritime wireless communication environment,the overall design of receiver synchronization module for physical layer of OFDM system is proposed and FPGA implementation is completed.And a scheme for reducing hardware implementation complexity is proposed for the frame synchronization module.This scheme redefines the decision function such that each complex multiplication operation can eliminate two addition operations.The result shows that the proposed solution reduces the occupancy of the FPGA lookup table and register resources by 49.7% and 32.8%,respectively,compared to the original scheme.更多还原